US20120028117A1 - Fluorinated binder composite materials and carbon nanotubes for positive electrodes for lithium batteries - Google Patents

Fluorinated binder composite materials and carbon nanotubes for positive electrodes for lithium batteries Download PDF

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US20120028117A1
US20120028117A1 US13/256,522 US201013256522A US2012028117A1 US 20120028117 A1 US20120028117 A1 US 20120028117A1 US 201013256522 A US201013256522 A US 201013256522A US 2012028117 A1 US2012028117 A1 US 2012028117A1
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composite material
suspension
electrode
weight
pvdf
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Dominique Plee
Bernard Lestriez
Sabrina Desaever
Dominique Guyomard
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Centre National de la Recherche Scientifique CNRS
Arkema France SA
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Centre National de la Recherche Scientifique CNRS
Arkema France SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/043—Processes of manufacture in general involving compressing or compaction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention relates generally to the field of the storage of electrical energy in secondary lithium batteries of Li-ion type. More specifically, the invention relates to a material for the positive electrode of an Li-ion battery, to its method of preparation and to its use in an Li-ion battery. Another subject matter of the invention is the Li-ion batteries manufactured by incorporating this composite electrode material.
  • the electrode material according to the invention can be used in a secondary Li-ion battery comprising a nonaqueous electrolyte, on which it confers excellent characteristics of capacity and cycling under high current density.
  • An Li-ion battery comprises at least one negative electrode or anode coupled to a current collector made of copper, a positive electrode or cathode coupled to a current collector made of aluminum, a separator and an electrolyte.
  • the electrolyte is composed of a lithium salt, generally lithium hexafluorophosphate, mixed with a solvent which is a mixture of organic carbonates which are chosen in order to optimize the transportation and the dissociation of the ions.
  • a high dielectric constant promotes the dissociation of the ions and thus the number of ions available in a given volume, whereas a low viscosity promotes ion diffusion, which plays an essential role, among other parameters, in the charge and discharge rates of the electrochemical system.
  • An electrode generally comprises at least one current collector on which is deposited a composite material which is composed of: an “active” material, as it exhibits an electrochemical activity with regard to lithium, a polymer, which acts as binder and which is generally a vinylidene fluoride copolymer for the positive electrode and aqueous-based binders, of carboxymethylcellulose type, or styrene-butadiene latexes for the negative electrode, plus an additive which conducts electrons, which is generally carbon black Super P or acetylene black.
  • lithium is inserted into the active material of the negative electrode (anode) and its concentration is kept constant in the solvent by the extraction of an equivalent amount of the active material of the positive electrode (cathode).
  • the insertion into the negative electrode is reflected by a reduction of the lithium and it is therefore necessary to contribute, via an external circuit, the electrons to this electrode originating from the positive electrode.
  • the reverse reactions take place.
  • the conventional active materials are graphite at the negative electrode and cobalt oxide at the positive electrode.
  • Li-ion batteries are used today above all in the fields of mobile phones, computers and lightweight equipment but a few niche markets exist, such as the space industry, aeronautical industry and defense applications.
  • electrochemical storage appears a method of choice in making possible optimum use and optimum management of the production of energy by the intermittent renewable energy sources which are solar power and wind power.
  • Li-ion batteries exhibit virtually the highest energy density among rechargeable systems and are thus widely envisaged as source of electrical energy in electric vehicles and hybrid vehicles in the future, in particular those which would make it possible to directly recharge via the mains.
  • Li-ion batteries retain some disadvantages, related in particular to safety (possibility of decomposition of the electrolyte and of the solvent with release of gas, risk of explosion and/or of ignition) and to the still high cost of the kWh stored, which has led to numerous studies on alternative active materials, both with the positive electrode (phosphates, various oxides, and the like) and with the negative electrode (silicon, tin, various alloys, and the like).
  • Cobalt oxide exhibits an advantageous voltage difference with respect to lithium, a good capacity and a very reasonable aging quality but runaway reactions can occur and be reflected by overheating, decomposition of solvent and electrolytes, indeed even explosions and fires, if the internal pressure exceeds the resistance of the casing of the battery. This characteristic renders the motor vehicle application out of the question. Furthermore, cobalt is now included among expensive materials and those of limited availability.
  • iron phosphate has a good capacity by weight of the order of 160 mAh/g, scarcely inferior to that of cobalt oxide, but, in terms of performance by volume, the difference is accentuated because the density of iron phosphate is only 3.5.
  • a second disadvantage is its low electrical conductivity and it is for this reason that it is supplied covered with a carbon-based coating.
  • CNTs carbon nanotubes
  • CNT in composite materials for a positive electrode is furthermore described in various documents, in particular in the patent applications US 2008/038635, JP 2003-331838, JP 2003-092105 or JP 07-014582.
  • the document CN 101 192 682 describes a secondary Li-ion battery comprising an anode composed of a mixture of a complex lithium oxide, such as a mixed Ni—Co—Li, Mn—Li or Mn—B—Li oxide, with carbon nanotubes as conductive agents in a portion of 0.1 to 3% by weight and a polymer binder, such as PVDF or PTFE.
  • a complex lithium oxide such as a mixed Ni—Co—Li, Mn—Li or Mn—B—Li oxide
  • carbon nanotubes as conductive agents in a portion of 0.1 to 3% by weight
  • a polymer binder such as PVDF or PTFE.
  • the document EP 2 034 541 describes a process for the preparation of composite materials for a positive electrode of a lithium battery comprising lithium manganate, CNTs, carbon black and a fluoropolymer binder.
  • the electrode active substance for a secondary lithium battery is preferably chosen from transition metal oxides, such as lithium cobalt oxide LiCoO 2 , lithium nickel oxide LiNiO 2 , lithium manganese oxide (LiMn 2 O 4 ) or mixed oxides based on several transition metals.
  • the invention relates to a composite material for a positive electrode of an Li-ion battery, comprising:
  • the compounds having polyanionic frameworks are mixed phosphates or silicates of lithium and of a metal atom M. More particularly, they are mixed phosphates.
  • the compounds having polyanionic frameworks have a structure of masicon or olivine type.
  • M is chosen from Fe, Mn or their combination.
  • the lithium insertion compound is LiFePO 4 .
  • the CNTs forming part of the structure of the composite material according to the invention have a fibrillar morphology. They generally have diameters of 10 to 50 nm, preferably of 10 to 20 nm, on average.
  • the length of the carbon nanotubes is generally of the order of 5-15 ⁇ m but some dispersing processes may reduce it, in particular ultrasound.
  • This conductive additive differs from the usual conductive additives, such as SP carbon, acetylene black or graphite, in a very high aspect ratio. The latter is defined as the ratio of the greatest dimension to the smallest dimension of the particles. This ratio is of the order of 30 to 1000 for CNTs, as opposed to 3 to 10 for SP carbon, acetylene black and graphite.
  • the CNTs play, in the electrode composite material, an important role with regard to maintaining the capacity as a function of the current density, maintaining the capacity in cycling, which allows excellent cycling stability, this being the case at high contents of active material (for example up to 94%) in the composite electrode material.
  • the carbon nanotubes forming part of the structure of the composite material according to the invention have a content of transition metals of less than 1000 ppm by weight, measured by conventional chemical analysis, and preferably of less than 500 ppm. Excessively high contents of transition metals are believed to reduce the lifetime of the batteries, in particular at high temperature, and to increase the operating risks. However, to produce such nanotubes can prove to be expensive and can result in excessive battery manufacturing costs. The Applicant Company has found, surprisingly, that some nanotubes comprising markedly greater proportions than those mentioned above do not present problems in practice.
  • crude carbon nanotubes comprising residues of synthesis catalyst have proved to be entirely usable in the composite material according to the invention; they exhibit an electrochemical signature in cyclic voltammetry such that a persistence and a complete reversibility of the oxidation/reduction phenomena are observed.
  • conductive additives can be added to the composite material: graphite, carbon black, such as acetylene black, SP carbon or carbon nanofibers.
  • commercial conductive additives meet this condition. Mention may in particular be made of the compounds Ensagri Super S® or Super P®, sold by Chemetals, or the VGCF nanofibers, sold by Showa Denko.
  • the polymer binder can be chosen from: polysaccharides, modified polysaccharides, latexes, polyelectrolytes, polyethers, polyesters, polyacrylic polymers, polycarbonates, polyimines, polyamides, polyacrylamides, polyurethanes, polyepoxides, polyphosphazenes, polysulfones, or halogenated polymers.
  • halogenated polymer of homopolymers and copolymers of vinyl chloride, of vinylidene fluoride, of vinylidene chloride, of tetrafluoroethylene or of chlorotrifluoroethylene, and copolymers of vinylidene fluoride and of hexafluoropropylene (PVDF-HFP).
  • the term “copolymer” is understood to mean, in the present text, a polymer compound obtained from at least two different monomers. Blends of polymers are also advantageous. Mention may be made of the blends of carboxymethylcellulose with styrene/butadiene, acrylic and nitrile rubber latexes. Water-soluble polymers are particularly preferred. In particular, aqueous latexes of fluorocopolymers or fluorohomopolymers are particularly preferred.
  • the polymer binder is chosen from the group: PVDF, PVDF/HFP or PVDF/PCTFE copolymers, blends of PVDF and of a PVDF comprising polar functional groups, and fluoroterpolymers.
  • the invention relates to a process for the preparation of an electrode composite material which comprises the following operations:
  • the polymer is introduced in the pure state or in the form of a solution in a volatile solvent; the CNTs are introduced in the pure state or in the form of a suspension in a volatile solvent.
  • the CNTs are those sold under the Graphistrength® C100 name by Arkema, exhibiting the following characteristics: the CNTs are multiwall nanotubes having from 5 to 15 walls, a mean external diameter ranging from 10 to 15 nm and a length ranging from 0.1 to 10 ⁇ m.
  • the carbon nanotubes are difficult to disperse. Nevertheless, by virtue of the process according to the invention, it is possible to distribute them in the electrode composite material in such a way that they form a meshwork around the particles of active material and thus play a role both of conductive additive and also of mechanical maintenance, which is important in order to accommodate the variations in volume during the charging/discharging stages. On the one hand, they provide for the delivery of the electrons to the active material particles and, on the other hand, due to their length and their flexibility, they form electrical bridges between the active material particles which move about as a result of their variation in volume.
  • the volatile solvent is an organic solvent or water or a mixture of organic solvent and of water. Mention may be made, among organic solvents, of N-methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO) or dimethylformamide (DMF).
  • NMP N-methylpyrrolidone
  • DMSO dimethyl sulfoxide
  • DMF dimethylformamide
  • the suspension can be prepared in a single stage or in two or three successive stages.
  • one embodiment consists of the mixing of all the constituents, followed by the mechanical dispersing stage.
  • one embodiment consists in preparing a first dispersion, comprising the solvent, the CNTs and optionally all or part of the polymer binder, using mechanical means, and in then adding, to this first dispersion, the other constituents of the composite material, this new suspension being used for the preparation of the final film.
  • one embodiment consists in preparing a dispersion comprising the CNTs and optionally all or part of the polymer binder in a solvent, in then adding the active material, in removing the solvent in order to obtain a powder and in then forming a new suspension by adding solvent and the remainder of the constituents of the composite material to this powder, this new suspension being used for the preparation of the final film.
  • a preferred method for forming and homogenizing the dispersion consists in preparing a suspension of solvent, of polymer and of CNT which is subjected to the mechanical dispersing process, before the addition of the active material.
  • Another preferred method for forming and homogenizing the dispersion consists in preparing a suspension of solvent and of CNT which is subjected to said mechanical dispersing process, before the addition of the binders and active material.
  • the level of performance achieved for the Li-ion battery incorporating the composite material of a positive electrode obtained according to the process of the invention results from the conditions of preparation of said material, in particular the stage of predispersing the CNTs by milling, and the quality of the dispersing, which is preferably carried out over a long period of time, generally of greater than 10 hours, which is not obvious to a person skilled in the art.
  • the quality of the dispersing is assessed on the basis of the values of the storage modulus G′, which is obtained by frequency rheological measurements, which measurements give access to two parameters G′ and G′′, respectively storage modulus and loss modulus.
  • the CNT suspension prepared according to the invention exhibits, for a frequency of 1 Hz, a storage modulus G′ as follows:
  • the film can be obtained from the suspension by any conventional means, for example by extrusion, by tape casting or by spray drying on a substrate, followed by drying.
  • a metal sheet capable of acting as collector for the electrode for example an aluminum sheet or grid treated with a corrosion-resistant coating.
  • the film on a substrate thus obtained can be used directly as electrode.
  • This film can optionally be made denser by application of a pressure (between 0.1 and 10 tonnes/cm 2 ).
  • the composite material according to the invention is of use in the preparation of electrodes for electrochemical devices, in particular in lithium batteries.
  • Another subject-matter of the invention is composed of a positive electrode of an Li-ion battery comprising at least one current collector on which is deposited a composite material according to the invention or obtained according to the process of the invention.
  • Another subject matter of the invention consists of an Li-ion battery incorporating said positive electrode.
  • a lithium battery comprises a negative electrode, composed of lithium metal, a lithium alloy or a lithium insertion compound, and a positive electrode, the two electrodes being separated by a solution of a salt, the cation of which comprises at least one lithium ion, such as, for example, LiPF 6 , LiAsF 6 , LiClO 4 , LiBF 4 , LiC 4 BO 8 , Li(C 2 F 5 SO 2 ) 2 N, Li[(C 2 F 5 ) 3 PF 3 ], LiCF 3 SO 3 , LiCH 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 F) 2 , and the like, in an aprotic solvent (ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl carbonate, and the like), the combined mixture acting as electrolyte.
  • aprotic solvent ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl carbonate, and the
  • the positive electrode is composed of the composite material, the active substance of which represents from 80% to 97%.
  • the content of polymeric binder is between 0.1 and 10% and the content of carbon nanotubes is between 1% and 2.5% by weight, preferably between 1.5% and 2.2% by weight, of the weight of the dry electrode.
  • the invention also relates to the use of a composite material comprising:
  • the invention also relates to the use of a composite material obtained according to the process described above in the manufacture of Li-ion batteries.
  • the composite material is composed of 94% by weight of C/LiFePO 4 with a carbon coating, the latter representing 1-3% of the total weight of C/LiFePO 4 , of 4% by weight of the PVDF binder supplied by Arkema under the Kynar® brand, 1 ⁇ 3 of which is composed of Kynar® ADX and 2 ⁇ 3 of which is composed of Kynar® HSV 900, and of 2% by weight of CNTs supplied by Arkema under the name Graphistrength® C100.
  • These nanotubes have a mean diameter of 20 nm and a length estimated at a few microns and their chemical composition shows that they comprise approximately 7% of inorganic ash resulting from the synthesis process.
  • the mixture is comilled in a jar made of chromium stainless steel with a volume of 250 ml, containing a mixture of beads made of chromium stainless steel with a diameter of 10 and 5 mm, by a planetary mill for 24 h. After drying at 120° C., the mixture is treated at 600° C. for 6 h in an atmosphere of argon (with 2% of H 2 ).
  • a first stage all of the CNTs participating in the composition of the composite material are first of all dispersed in NMP using a bead mill (Pulverisette 7, Fritsch).
  • the conditions of the dispersing are 700 revolutions/minute and a 12.5 ml milling chamber containing three beads with a diameter of 10 mm, 0.360 ml of NMP and 8 mg of CNT.
  • the duration of the dispersing varies from 6 to 48 h.
  • the C/LiFePO 4 particles (376 mg), 16 mg of PVDF and 0.640 ml of NMP are added to the dispersion of the CNTs and everything is mixed by comilling at 700 revolutions/minute for 1 h 30.
  • the composite material constitutes 29% by weight of the suspension, the remainder being NMP.
  • the electrode is prepared by coating the suspension comprising the composite onto a current collector made of aluminum with a thickness of 25 ⁇ m.
  • the height of the scraper of the coating machine is set at 180 ⁇ m.
  • the electrode is dried overnight in an oven at 70° C. It is then made dense under 62.5 MPa. It is subsequently again dried in an oven at 70° C. overnight and finally at 100° C. under vacuum for 1 h. After drying, the amount of electrode deposited per unit of surface area of current collector is measured: 4 mg/cm 2 .
  • the electrode thus obtained was fitted to a battery having, as negative electrode, a sheet of lithium metal rolled onto a current collector made of nickel, a separator made of fiber glass and a liquid electrolyte composed of a 1M solution of LiPF 6 dissolved in a 1:1 mixture of ethylene carbonate and dimethyl carbonate (EC/DMC).
  • EC/DMC ethylene carbonate and dimethyl carbonate
  • the evaluation of the electrochemical performance was carried out in the potential range 2-4.3 V vs. Li + /Li, in galvanostatic mode.
  • a current I of 1 A/g corresponds to a 6C rate (duration of charging or discharging 10 minutes).
  • FIG. 1 represents the change in the capacity Q (in mAh/g) at a 6C rate (1 A/g) as a function of the duration of the dispersing of the CNTs. The best electrochemical performance is obtained for an optimum dispersing time of 15 h.
  • FIG. 2 gives the rheological characteristics of the CNT dispersion after milling for 15 h.
  • a solids content of CNT 8 mg in 0.360 ml of NMP, an optimum electrochemical performance is obtained when the storage module G′ reaches a value of at least 250 Pa in the frequency range 0.1 to 100 Hz.
  • composition of the composite material of this example is identical to that of example 1.
  • the preparation differs from that given in example 1 in that the PVDF binder is introduced, in the powder form, during the first stage, that is to say during the dispersing of the CNTs.
  • all of the CNTs and of the PVDFs participating in the composition of the composite material are first of all dispersed in NMP using a bead mill (Pulverisette 7, Fritsch).
  • the conditions of the dispersing are 700 revolutions/minute and a 12.5 ml milling chamber containing three beads with a diameter of 10 mm, 0.360 ml of NMP, 8 mg of CNT and 16 mg of PVDF.
  • the duration of the dispersing varies from 6 to 48 h.
  • the C/LiFePO 4 particles (376 mg) and 0.640 ml of NMP are added and everything is mixed by comilling at 700 revolutions per minute for 1 h 30.
  • the composite material constitutes 29% by weight of the suspension, the remainder being NMP.
  • the electrode and the battery are subsequently prepared and the electrochemical performance is evaluated as in example 1.
  • FIG. 3 represents the change in the capacity Q (in mAh/g) at a 6C rate as a function of the duration of the dispersing of the CNT+PVDF mixture. The best electrochemical performance is obtained for an optimum dispersing time of 24 h.
  • composition of the composite material of this example is identical to that of example 1.
  • the preparation differs from that given in example 1 in the following characteristics: during the first stage, the duration of the dispersing of the CNTs is 15 h; during the second stage, the composite material constitutes 32% by weight of the suspension; and, during the third stage, the height of the scraper is set at 300 ⁇ m and the densifying pressure is 750 MPa. After the third stage, the amount of electrode deposited per unit of surface area of current collector is measured: 7 mg/cm 2 .
  • the electrode (a) thus obtained was fitted to a battery having, as negative electrode, a sheet of lithium metal rolled onto a current collector made of nickel, a separator made of fiber glass and a liquid electrolyte composed of a 1M solution of LiPF 6 dissolved in 1:1 EC/DMC.
  • the electrochemical performance was measured and compared with those of similar batteries in which the positive electrode is an electrode having the following initial composition:
  • the amount of electrode deposited per unit of surface area of current collector is 7 mg/cm 2 for (b) and (c).
  • FIG. 4 represents the change in the capacity Q (in mAh/g) as a function of the current by weight.
  • the correspondence between the two curves and the samples is as follows:
  • Curve - ⁇ -- ⁇ - sample a according to the invention
  • Curve - ⁇ -- ⁇ - comparative sample b
  • Curve - ⁇ -- ⁇ - comparative sample c
  • the comparison of the curves shows better maintenance of the capacity as a function of the current density for the electrode according to the invention.
  • the capacity restored at a 6C rate is 120 mAh/g of C/LiFePO 4 with the CNTs, 100 mAh/g with the acetylene black and 85 mAh/g with the VGCFs.
  • the restored capacity is related to the weight of electrode, the following results are obtained: 113 mAh/g of electrode with the CNTs, 91 mAh/g with acetylene black and 78 mAh/g with the VGCFs, which demonstrate the superiority of the electrode (a) according to the invention.
  • composition of the composite material of this example is 94.3% of C/LiFePO 4 , 1.7% of CNT and 4% of PVDF.
  • the material was prepared in the same way as the material of example 3.
  • the electrode (a) thus obtained was fitted to a battery having, as negative electrode, a sheet of lithium metal rolled onto a current collector made of nickel, a separator made of fiber glass and a liquid electrolyte composed of a 1M solution of LiPF 6 dissolved in 1:1 EC/DMC.
  • the electrochemical performance was measured and compared with those of similar batteries in which the positive electrode is an electrode having the following initial composition:
  • FIG. 5 represents the change in the capacity Q (in mAh/g) as a function of the cycle number for the three samples (a), (b) and (c).
  • the charge current by weight corresponds to a C rate and the discharge current by weight corresponds to a 2C rate.
  • Curve - ⁇ -- ⁇ - sample a according to the invention
  • Curve - ⁇ -- ⁇ - comparative sample b
  • Curve - ⁇ -- ⁇ - comparative sample c
  • composition of the composite material of this example is 94.3% of C/LiFePO 4 , 1.7% of CNT and 4% of PVDF.
  • the material was prepared in the same way as the material of example 4, except for one difference, namely that the CNTs were purified so as to reduce the iron content. After treatment, this content was found to be 215 ppm.
  • the electrode (a′) thus obtained was fitted to a battery having, as negative electrode, a sheet of lithium metal rolled onto a current collector made of nickel, a separator made of fiber glass and a liquid electrolyte composed of a 1M solution of LiPF 6 dissolved in 1:1 EC/DMC.
  • the electrochemical performance was measured and compared with those of similar batteries in which the positive electrode is an electrode having the following initial composition:
  • Table 1 below shows the comparison in performances for the four systems, in initial and final capacities.
  • composition of the composite material of this example is similar to that of examples 1 to 3, 94% of C/LiFePO 4 , 2% of CNT and 4% of PVDF. It is prepared as follows: all of the CNTs participating in the composition of the composite material are first of all dispersed in NMP. On conclusion of the dispersing, C/LiFePO 4 particles and NMP are added and everything is mixed by comilling. The NMP is subsequently removed by drying and the powder obtained is recovered. It is subsequently dispersed in a solution of PVDF in NMP.
  • a first stage all of the CNTs participating in the composition of the composite material are first of all dispersed in NMP using a bead mill (Pulverisette 7, Fritsch).
  • the conditions of the dispersing are 700 revolutions/minute for 15 hours and a 12.5 ml milling chamber containing three beads with a diameter of 10 mm, 0.360 ml of NMP and 9.6 mg of CNT.
  • the C/LiFePO 4 particles (447.4 mg) and 0.640 ml of NMP are added to the dispersion of the CNTs and everything is mixed by comilling at 700 revolutions per minute for 1 h 30.
  • the suspension is dried in an oven at 70° C. overnight, on conclusion of which a powder is recovered composed of 2.1% by weight of CNT and 97.9% by weight of C/LiFePO 4 .
  • this powder and 19 mg of PVDF are dispersed in 1 ml of NMP by comilling at 700 revolutions per minute for 1 h 30.
  • the composite material constitutes 32% by weight of the suspension, the remainder being NMP.
  • the electrode is prepared by coating the suspension comprising the composite onto a current collector made of aluminum with a thickness of 25 ⁇ m.
  • the height of the scraper of the coating machine is set at 300 ⁇ m.
  • the electrode is dried in an oven at 70° C. overnight. It is then made dense under 750 MPa. It is subsequently again dried in an oven at 70° C. overnight and finally at 100° C. under vacuum for 1 h. After drying, the amount of electrode deposited per unit of surface area of current collector is measured: 9 mg/cm 2 .
  • the electrode thus obtained was fitted to a battery having, as negative electrode, a sheet of lithium metal rolled onto a current collector made of nickel, a separator made of glass fiber and a liquid electrolyte composed of a 1M solution of LiPF 6 dissolved in 1:1 EC/DMC.
  • FIG. 6 represents the change in the capacity Q (in mAh/g) as a function of the cycle number at a C/5 rate and, in discharge, at a D/2.5 rate.
  • FIG. 7 represents the change in the capacity Q (in mAh/g) as a function of the current by weight. It is observed that the composite material according to the invention exhibits a good electrochemical performance.
  • Curve - ⁇ - sample according to the invention of example 6
  • Curve - ⁇ - sample according to the invention of example 7
  • composition of the composite material of this example is 94% C/LiFePO 4 , 2% CNT and 4% of a mixture of carboxymethylcellulose (CMC) and styrene/butadiene (SBR).
  • CMC carboxymethylcellulose
  • SBR styrene/butadiene
  • a first stage all of the CNTs participating in the composition of the composite material are first of all dispersed in NMP using a bead mill (Pulverisette 7, Fritsch).
  • the conditions of the dispersing are 700 revolutions/minute for 15 hours and a 12.5 ml milling chamber containing three beads with a diameter of 10 mm, 0.360 ml of NMP and 9.6 mg of CNT.
  • the C/LiFePO 4 particles (447.4 mg) and 0.640 ml of NMP are added to the dispersion of the CNTs and everything is mixed by comilling at 700 revolutions per minute for 1 h 30.
  • the suspension is dried in an oven at 70° C. overnight, on conclusion of which a powder is recovered composed of 2.1% by weight of CNT and 97.9% by weight of C/LiFePO 4 .
  • this powder and 19 mg of CMC+SBR are dispersed in 1 ml of deionized water by comilling at 700 revolutions per minute for 1 h 30.
  • the composite material constitutes 32% by weight of the suspension, the remainder being deionized water.
  • the electrode is prepared by coating the suspension comprising the composite onto a current collector made of aluminum with a thickness of 25 ⁇ m.
  • the height of the scraper of the coating machine is set at 300 ⁇ m.
  • the electrode is dried at ambient temperature overnight. It is then made dense under 750 MPa. It is subsequently dried at 100° C. under vacuum for 1 h. After drying, the amount of electrode deposited per unit of surface area of current collector is measured: 6 mg/cm 2 .
  • the electrode thus obtained was fitted to a battery having, as negative electrode, a sheet of lithium metal rolled onto a current collector made of nickel, a separator made of glass fiber and a liquid electrolyte composed of a 1M solution of LiPF 6 dissolved in 1:1 EC/DMC.
  • FIG. 6 represents the change in the capacity Q (in mAh/g) as a function of the cycle number at a C/5 rate and, in discharge, at a D/2.5 rate.
  • FIG. 7 represents the change in the capacity Q (in mAh/g) as a function of the current by weight. It is observed that the composite material according to the invention exhibits a good electrochemical performance.
  • Curve - ⁇ - sample according to the invention of example 6
  • Curve - ⁇ - sample according to the invention of example 7
  • a button cell is assembled in the following way, comprising:

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FR0901279A FR2943463B1 (fr) 2009-03-19 2009-03-19 Materiaux composites a base de liants fluores et nanotubes de carbone pour electrodes positives de batteries lithium.
PCT/FR2010/050485 WO2010106292A1 (fr) 2009-03-19 2010-03-18 Materiaux composites a base de liants fluores et nanotubes de carbone pour electrodes positives de batteries lithium

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US10615405B2 (en) 2015-03-03 2020-04-07 Arkema France Electrodes of li-ion batteries with improved conductivity
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US11664485B2 (en) * 2017-05-12 2023-05-30 Lg Energy Solution, Ltd. Method for manufacturing lithium secondary battery
US11367862B2 (en) 2018-08-28 2022-06-21 Samsung Electronics Co., Ltd. Cathode and lithium battery including the same
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WO2010106292A1 (fr) 2010-09-23
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KR20110136867A (ko) 2011-12-21

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